Solve for a
a=15
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a+2a=\frac{90}{2}
Divide both sides by 2.
a+2a=45
Divide 90 by 2 to get 45.
3a=45
Combine a and 2a to get 3a.
a=\frac{45}{3}
Divide both sides by 3.
a=15
Divide 45 by 3 to get 15.
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